1. Field of the Invention
The present invention relates to an image processing apparatus and method and to a computer program for processing video signals, such as received television signals. In particular, the present invention relates to an image processing apparatus and method and to a computer program for recording a video signal, such as a received television signal, onto an external medium.
More specifically, the present invention relates to an image processing apparatus and method and to a computer program for recording currently displayed video, such as a broadcasted program, onto an external medium as a still image. In particular, the present invention relates to an image processing apparatus and method and to a computer program for recording a still image extracted from a currently displayed video signal onto an external medium so that the recorded still image can be repeatedly used.
2. Description of the Related Art
In the modern information society, broadcasting technologies play important roles. In particular, television (TV) broadcasting that allows direct delivery of audio and video information to subscribers has a large influence. The broadcasting technologies include a wide range of technologies, such as signal processing, signal transmission and reception, and audio and video information processing. Video signals are carried via a variety of media, such as radio waves, e.g., terrestrial and satellite broadcasting waves, cable TV broadcasting, and computer communication.
Due to the wide prevalence of TVs that have been introduced into most houses, broadcasted content delivered from each broadcast station is accessed by the general public. The broadcasted content may also be received and recorded so that the recorded content can be played back at any time, or a memo may be attached to a still image of currently displayed video.
Generally, TV sets have a function for providing a still image of currently displayed video using a “memo” button on a remote control unit. In response to an instruction to activate the video memo function from a user using the remote control unit, currently displayed video is captured as a still image, and the captured still image is displayed on, for example, a sub-screen (see, for example, Japanese Unexamined Patent Application Publication No. 2002-44544). The memo function allows the user to use information included in the supplied video signal without performing any time-consuming operation, and prevents the user from missing displayed video information. The memo function is a temporary display function using a field memory in an internal signal processing device of the TV set, and does not allow an identical still image to be displayed many times.
A still image is typically stored as a computer file using a JPEG (Joint Picture Experts Group) format. JPEG is an image data format in which 24-bit data is recorded by separating brightness signal components and chrominance signal components, and JPEG-compressed data is expanded using a combination of ADCT (adaptive discrete cosine transformation) and Huffman coding. A JPEG image portion may be recorded together with Exif data indicating photographic conditions, etc. The auxiliary Exif information includes user information tags that can be used by a user.
When a digital video camera records a still image as a JPEG file, information indicating the vendor name and the product name is also recorded in user information tags. However, TV sets do not have a function for converting the video currently displayed on the TV set into a JPEG still image file and recording the JPEG file onto an external medium.
TV sets often play back JPEG files that are photographed using digital still cameras and that are recorded onto memory card media. In decoding a JPEG file, however, only information having higher recording compatibility levels than the pseudo-requirements defined in the Exif standard is used, and the information included in the user information tags, which need not be recognized, is not used to decode the JPEG file or to display the still image.
Various type of displays incorporated in TV sets, such as a CRT (Cathode Ray Tube), a PDP (Plasma Display Panel), and an LCD (Liquid Crystal Display), have variations in the number of displayed pixels, and the image signal processing methods may differ from one model to another. Thus, the optimum image signal processing method for displaying the same image source depends upon each model. In order to record a still image using a JPEG format, bitmap data is compressed, thus inevitably causing degradation in the image quality of the reproduced data.
A JPEG file captured using a digital camera may be recorded with exposure conditions, etc., in header information. The condition information may be used to select processing for an image signal to be displayed in order to reduce degradation in the image quality caused by the signal processing other than data compression. However, a TV set performs JPEG conversion on video information in a uniform manner because no Exif information indicating the state of the original image is recorded. Thus, the reproducibility of the playback image with respect to the recorded image is not increased.
A motion video data recording method for extracting a still image from motion video to obtain desired image data is described in, for example, Japanese Unexamined Patent Application Publication No. 2000-333130. In this method, the quality of an image to be recorded is changed in response to an instruction to change the image quality while capturing motion video to reduce the amount of data to be recorded, which is not related to recording and playback of a video signal currently received by a TV set as a still image.